This invention relates to filter apparatuses of the type having elongate tubular filter bags for removing particulate material from a moving air or gas stream. More particularly, the invention is concerned with an improved air diffuser construction positioned in an elongate supporting cage which supports a surrounding tubular filter bag thereon.
In the aforementioned copending application there is disclosed a technique for cleaning gas permeable filter bags which normally collect dust, soot and other particulate material on the exterior surfaces thereof as the filtered air is exhausted through the open outlet ends of the filter bags, and wherein in addition to the usual tubular supporting cage within each tubular filter bag, a hollow, perforated, air diffuser tube is provided which extends longitudinally within each cage and the respective filter bag and communicates with the outlet end of the bag so that, when a periodic reverse purge flow of air is directed into the outlet end of the filter bag, the air is diffused by the diffuser tube and more uniformly distributed throughout the filter bag. Such more uniform distribution of the reverse purge air flow results in highly effective cleaning of the filter bag while also reducing excessive flexing of the filter bag and reducing abrasive wear thereof, thereby increasing the efficiency of the filter apparatus and significantly increasing the life of the filter bag.
In the early development of the air diffuser of said copending application, perforated air diffuser tubes of convolute form were used, i.e., they were made from a perforated metal sheet whose opposite longitudinal edges were overlapped and interconnected, as by welding and/or riveting to form a seam extending along the length of and parallel to the axis of the diffuser tube. While convolute air diffuser tubes have performed quite well for diffusing and distributing the reverse purge flow of air throughout the respective filter bags during the cleaning operations, it has been found that since the longitudinal seam of each of such convolute air diffuser tubes is imperforate, the seam tends to "blank out" or inhibit the flow of the reverse purge of air outwardly along an adjacent narrow area of the length of the respective tubular filter bag. Also, since it is desirable that the diffuser tube is provided throughout with relatively small, closely spaced perforations, it has been necessary to construct such convolute diffuser tubes of relatively heavy gauge sheet metal so that they would not bend easily or become damaged otherwise in the normal handling of the same during their manufacture, storage, and installation.
Accordingly, it is an object of this invention to provide a filter apparatus of the type described with air diffuser tubes of improved rigidity and stability and which substantially eliminates the "blank-out" problem presented by the longitudinal seams of the convolute air diffuser tubes used heretofore.
It is another object of this invention to provide an air diffuser tube of such construction that it may be made from a relatively lighter weight sheet metal as compared to the sheet metal used heretofore, and additionally has improved rigidity and stability for more effectively retaining its shape and integrity during normal handling and use and furthermore presents a more economically manufactured product.
According to the invention, filter apparatus of the type described is provided with a hollow air diffuser tube formed from a perforated strip of helically wound sheet metal and extending longitudinally within each filter bag supporting cage of the filter apparatus, and adjacent edges of the helically wound strip are interconnected by a seam in which the adjacent edges of the strip overlap each other in interlocking relationship. Thus, the seam extends helically around the air diffuser tube and provides a thickened area to impart rigidity and strength to the air diffuser tube permitting the use of a relatively thin gauge sheet metal in the manufacture of the air diffuser tube.